1. Field of the Invention
The present invention relates in general to operator stations having two control devices mounted on a common enclosure which must be actuated by two hands, and in particular to two-hand operator stations mounted on a common enclosure which do not require mechanical force to operate because a pushless sensing device is used to sense each hand.
2. Discussion
Run bars produce one or more electrical start signals for an automatic machine when the two spaced-apart buttons located on the run bar are simultaneously depressed. Conventional run bars, such as the type shown in FIG. 1, may be used with virtually any kind of automatic machine, from mechanical or hydraulic power presses, to assembly machines, transfer machines, milling machines, broaching or grinding machines, welding machines, or materials handling equipment, testing machines, and the like. The term "automatic machine" as used herein thus includes any type of machinery or industrial equipment which is automated in whole or in part. By "automated in whole or part," I mean that one or more functions or motions of the machinery or equipment are performed with the assistance of some form of non-human energy. Such energy could be electricity, hydraulic or pneumatic energy, photonic power such as laser beams or other concentrated light, magnetic or chemical energy, mechanical energy, or still other forms of energy.
Conventional run bars, such as the type shown in FIG. 1, are typically used in three different situations involving automatic machines. First, for an automatic machine that is operated by or attended to by one person, only one run-bar is used. Second, for an automatic machine operated by or attended to by two or more persons simultaneously, one run-bar will be provided for each person. In order to initiate the cycle or sequence of automatic operations, all of the operators must simultaneously actuate their respective run bars, to ensure that the hands of all of the operators are in a safe position, i.e., on the run bars. Third, there are certain kinds of automatic machines where the machines run continuously once started, but nevertheless are manually loaded and/or unloaded with parts or materials. Where such machine has a pinch point or other hazard during each cycle of the machine or each cycle of its load/unload mechanism, the operator is normally required to place his or her hands on the buttons of run bar during a certain portion of the machine's cycle when a pinch point or other hazard exists. In this situation, the run bar provides one or more signals which indicate to the control system of the automatic machine that the machine may continue running. Thus, it should be understood that the phrase "operating an automatic machine" is also used very broadly herein and is intended to include at least all of the following: (1) initiating a cycle, a sequence of one or more operations or cycles of the automatic machine; (2) participating in initiating a cycle, or sequence of one or more automatically performed operations or cycles of a machine; and (3) providing one or more signals to permit an automatic machine to continue to operate automatically.
FIG. 1 shows a conventional run bar apparatus commercially available from Control Devices, Inc. of Flint, Mich., the assignee of the present invention. This run bar 30 includes an elongated enclosure assembly 32 comprised of a cover 34 and base cabinet 36, left and right heavy-duty palm buttons 38 provided with metal guard rings 42 and 44, and an unguarded stop button 46 mounted in the center of the cover 34. The run bar also includes a four-hole mounting plate 48 located on the underside of the base cabinet 32 and an electrical connector assembly 50 including an electrical cable 52 which is mounted on the backside of the base cabinet 32. Conventional self-retaining screw-operated cover clamps 54 are also provided for holding the hinged cover 34 in its closed position on top of the cabinet 32. The run bar 30 may be supported at any desired height convenient for the operator by use of a pedestal 56 which is fastened to the four-hole mounted plate 48 by suitable fasteners such as bolts 58. The pedestal 56 may be fastened to the floor with lag bolts passing through holes 60 in the base 62 of the pedestal 56.
Machine designers and suppliers typically specify heavy-duty palm buttons for run bars, because they are subject to heavy use. Also, most suppliers of such palm buttons prefer to put fairly strong return springs in the buttons to help them last in heavy-duty use environments. This tends to increase the effort required to be exerted by operators.
One complaint made by some workers who use run bars is that the repetitive motion of pressing the buttons of a run bar can generate fatigue. Also, some workers claim that such repetitive motion with their hand aggravates a medical condition called Carpal Tunnel Syndrome. This condition is an inflammation associated with the naturally lubricated sheathing of the tendons within the wrists, which results in pain when such tendons in the sheathing are moved.
In light of the foregoing problems, it is an object of the present invention to provide a two-hand run bar apparatus which does not require any pressure or force from the operator's hands to actuate. It is a related object of the present invention to provide a run bar which does not even need to be physically touched in order to operate.
It is still another object of the present invention to provide a run bar which detects the presence of the operator's hands in the hand actuation regions of the run bar without requiring the operator to overcome a mechanical spring force. It is a further object of the present invention to provide another two-hand run bar which only needs to be contacted very lightly to operate.